1. Field of the Invention
This invention relates to roof drills used in drilling holes in the roof of a coal mine shaft for installation of roof bolts. More particularly it relates to a drill assembly that enables: (1) better removal of the dust created during drilling and (2) the ability to transmit increased drilling force to the bit through a strengthened shank thereby enabling a faster drilling speed.
2. Prior Art
Prior art "through the steel" drill assemblies do not have the rake of the drill portion designed such that the dust is created during drilling and directed downwardly from the drill bit is centered over the channels that communicate from the outside of the drill rod to the inner opening in the tubular drive rod. Vacuum is applied to the inner opening to remove the dust, however, since the dust was not centered over the channels removal was often hindered thus reducing penetration rates. It is believed, therefore, that a new drill assembly that enables the dust directed from the drill bit to be centered over the channels that communicate from the outside of the drive rod to the inner opening to which vacuum is applied enabling essentially all of the dust to be removed unhampered via the inner opening by the vacuum, would be an advancement in the art. This design also allows for a more massive shank to be used thus allowing higher cutting forces to be transmitted to the bit.